FIELD OF THE INVENTION
This invention relates to a method and apparatus for mixing foundry aggregate (hereinafter referred to by the expression "sand") and binder to provide a mixture for making moulds and cores to be used in casting operations.
The invention is concerned with the provision of a mixture in which sand is mixed with a curable binder which may be a synthetic resin, and a catalyst which accelerates the curing and setting of the binder so as to speed up production of castings by cutting down on the time taken for the setting of moulds and cores. Over recent years the aim of manufacturers of binders and catalysts has been to produce such materials which will further shorten the curing and setting time and binders and catalysts have now been brought into use to provide a mixture setting time of only a few minutes, which time may in some cases be less than five minutes. In particular, there has been considerable development in this direction in the field of cold setting binders, so called because they do not require any heating to effect curing which takes place very rapidly "in the cold." The present invention is particularly, but not exclusively, concerned with method and apparatus for mixing foundry sand with these cold setting binders and catalysts.
The introduction of these rapid hardening or rapid setting binders has brought about complications in connection with the apparatus which is used for mixing the sand, binder and catalyst mixture because of the fact that the curing or setting commences as soon as the binder and catalyst are brought together and thus the process of mixing and discharging of the mixture into mould boxes and core boxes must be rapid enough to avoid any premature setting of the sand mixture in the apparatus itself which would lead to clogging and eventual stoppage of the apparatus. A further drawback to the use of these rapid setting binders is that any residual mixture in the apparatus will set and clog the apparatus if it is not cleared out rapidly.